1. Field of the Invention
The present invention relates to a semiconductor device and a method for fabricating the same. More particularly, the present invention relates to a semiconductor device having a multi-bridge-channel (MBC) metal oxide semiconductor field effect transistor (MBC) formed by self-alignment and a method for fabricating the same.
2. Description of the Related Art
To more highly integrate semiconductor devices, a length of gate channels is decreased. A short channel length, however, generates several problems, such as a short channel effect, a fine pattern formation, and limitations on operation speed. The short channel effect is a particularly severe problem. For example, an electric field increase in a vicinity of a drain region causes a punch-through, in which a drain depletion region penetrates up to an electric potential wall in a vicinity of a source region. Further, thermal electrons cause an avalanche and a vertical electric field decreases mobility of carriers.
In an effort to eliminate the short channel effect, several gate structures including a MOST having a multi-bridge-channel (MBC) have been suggested. A conventional MBC includes, e.g., a gate electrode layer enclosing a plurality of thin channel semiconductor layers having a rectangular shape. In such a conventional MBC, a channel semiconductor layer has a very wide area. Thus, the MBC is under a small influence of an electric field in the vicinity of a drain region, which eliminates the short channel effect.
Such a conventional MBC, however, is subjected to two separate photoetching processes including a process for forming the channel semiconductor layer and a process for forming the gate electrode covering and surrounding the channel semiconductor layer. Disadvantageously, misalignments are generated between the gate electrodes and the channel semiconductor layers during these processes.